1. Field of the Invention.
This invention relates to devices for providing an afterburn or combustion of exhaust gases which are created by combustion in stoves such as wood and coal burning stoves. The invention also relates to devices for directing draft air flowing through a draft air flue into the stove pipe of a stove.
2. Discussion of the Prior Art.
Wood burning and coal burning stoves have been in existence for hundreds if not thousands of years. After suffering a setback in popularity, wood and coal stoves most recently are making a comeback.
The well known Franklin-type stove however, suffers considerable inefficiencies and poses certain dangerous conditions. The heat is too rapidly lost in such stoves, creosote pitch build-up is significant which could cause chimney fires, and there is no overall control of the fire burning in the stove. Furthermore, the burning of wood is incomplete resulting in the production of volatile gases, carbon monoxide, and other undesirable gases such as sulphur dioxide. Pitch build-up in the stove pipe results from the deposition of creosote vapors and is due to a number of factors such as incomplete combustion of the creosote vapors in the exhaust, the existence of high humidity in the exhaust, and the coolness of the stove pipe.
Numerous advances over the conventional Franklin-type stove have been made to make them more air tight and to provide greater control over the burning of logs, to allow the logs to burn longer, to retain the heat in the fireplace for a longer period of time and not to lose the heat up the chimney. One approach was to use the downdraft design for feeding air to the primary fire in order to drive the smoke back into the fire. Such downdraft designs were difficult to tend. However, the problem of pitch build-up, the problem of creating significant pollutants such as ash and carbon monoxide still exist. Even with such improvements, however, the hazard of flue fires caused by pitch build-up is great.
Secondary combustion of the exhaust gases, by providing a separate chamber, by providing a separate air supply or by providing both have been used with limited success. It is desirable to create a second combustion area in addition to the primary combustion area. In such a secondary area, the pollutants can be significantly reduced, carbon monoxide can be converted to carbon dioxide and pitch build-up from condensation of creosote gases can be minimized. One approach to providing an afterburn or secondary combustion area is to provide an inlet of air into the region of the stove near where the stove connects with the stove pipe. In these prior art approaches, room air is inputted into an area of below or near the area of the afterburn or secondary combustion. Such approaches, however, also provide air to the primary area of combustion and thus may cause an increased rate of combustion and also cause significant loss of heat to occur upwardly through the chimney. Also, this type of approach increases heat production, increases exhaust gas rise rate and increases the overall combustion rate. Back puffing of smoke also may occur, resulting in possible backflash.
The present invention seeks to improve the efficiency of combustion of the creosote vapors in the afterburn area thereby significantly reducing the build-up of pitch, seeks to reduce the number of pollutants in the atmosphere, seeks to minimize the production of carbon monoxide and to encourage the production of carbon dioxide, seeks to preserve the retention of heat in the fireplace, seeks to decrease the rate of combustion of the logs in the fireplace, by providing a regulated amount of air to the region of the afterburn or secondary combustion from above the area of secondary combustion. The present invention uses air from a source of draft air located in the stove pipe above the area of afterburn.
Under the teachings of the present invention, the vacuum created by the fire and the rising gases pulls a portion of the draft air downwardly to the region of second combusion. This draft air which is pulled down is pre-heated and mixes with the exhaust gases to provide further combustion of the exhaust gases in a region near the connection of the stove pipe to the stove within the stoves heat exchange area. The addition of the draft air from above does not increase the rate of primary combustion in the stove. Furthermore, the draft air delivered downwardly is regulated being affected by the pressure in the stove pipe. And, because the source of air for the secondary combustion is delivered from the stove pipe downwardly, the heat in the stove is significantly retained over prior approaches because the hot vapors remain in the stove for a longer period of time. While this is occurring, the primary fire can be controlled to a desired rate of combustion since its source of air is not affected by the source of air for the secondary combustion.
Also under the teachings of the present invention, substantially all of the draft air is delivered upwardly in the stove pipe to maintain the pressure in the stove pipe (and not to draw through the fire on the primary intake) and to reduce the overall temperature of the pipe.